Electrooptical image production



Aug. 28, 1934.

J. w. HORTON 1,971,675

ELECTROOPTICLAL IMAGE PRODUCTION Filed Aug. 7, 1931 2 Sheets-Sheet TAPEmmsM/ T7FH .372

TAPE HJLLER AND PERFORATOR /Nl/EN 70/? J. W HORTON var 41W ATTORNEY Aug.28, 1934. J w HORTQN 1,971,675

ELECTROOPTIGAL IMAGE PRODUCTION Filed Aug. 7,1931 2 Sheets-Sheet 2 //v0/? J W HORTON Patented Aug. 28, 1934 1,971,675 ELECTROOPTICAL IMAGEPRODUCTION Joseph W. Horton, Cambridge, Mass, assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of NewYorkApplication August 7, 1931, Serial No. 555,669 13 Claims. (01. itsi Thisinvention relates to electro-optical sys tems and particularly tosystemsfor reproducing pictures by the use of telegraph code signals. 4The invention providesan improved system for s the electricaltransmission of pictures or the production of images at a distant pointunder control of transmitted currents corresponding to the tone valuesof the elemental areas of a picture or other object.

In accordance with the invention, there is pro duced a current having analternating component the amplitude of which periodically changes fromone value to another and the amplitude of this current is controlledinaccordance with the tone vvalues of successively scanned elemental areasof the production of an image. A system in which the scanning lightbeamis uniformly interrupted is disclosed and claimed in a copendingapplication of J. H. Bollman Serial No. 553,098, filed July 30.25, 1931.l a

In a specific embodiment of the invention, herein shown and describedfor the purpose of illustration, means are provided for directing upon alight sensitive element a beam of light which is .caused to vary inaccordance with the tone values of the "successive elemental areas of apicture or object an image of which is to be produced. There is provideda rotating disc making a single revolution in the period required forscanning a single 40, elemental area and having apertures thereinarranged along an arc of a circle for interrupting the beam of light ata high frequency so that a high frequency current modulatediii-accordance with the tone values of the picture or object is producedin the circuit associated with the light sensitive cell. Theaperturesare omitted over a portion of the circle, so that the light beam isinterrupted for a comparatively long period between the scanning ofsuccessive elemental areas. This modulated 1- high frequency current,after being amplified by an alternating current amplifier which ispreferably associated with a tuned circuit to increase theamplificationefficiency, is impressedthrough a transformer, upon a plurality ofalternating 5 current amplifier vacuum tubes connected in .Ior punchedin the tapefor subsequently controlling parallel and biased so as tooperate over different ranges of impressed electromotive force; respec--tively'. The output circuit of each of these vacuum tubes is coupledthrough a transformer to a plurality of rectifier vacuum tubes, whichare 69 biased so as to operate over different values of impressedelectromotive force, respectively. An electromagnetic relay is connectedin the output circuit of each of the rectifier vacuum tubes.

After the scanning of each elemental area the 66 scanning light beam isinterrupted for a relatively long period, as pointed out above, so thatall of the relays are released prior to the scanning of the succeedingelemental area. There is no need of employing relays of such accuracythat they operate or release in response to small changes of currentsuch as are produced when scanning portions of a picture or otherobject, the successive elemental areas of which differ only slightly intone value. These relays control the selection of code combinations oftelegraph signals to be punched in a tape or transmitted directly, saidcode combinations corresponding to the tone' values of the elementalareas of the picture or object.

, A detail description of an illustrative embodi-' ment of the inventionfollows, reference being made to the accompanying drawings in which,

Figs. 1 and 2 show diagrammatically the transmitting andreceiving'stations of a code telegraph 35 1 picture reproducing systemin accordance with the present invention; i

Fig. 3 is a plan view of an apertured disc such as may be employed inthe system shown in Fig.

1 forinterrupting the scanning light beam. 0

Figs. 1 and 2 when placed side by side, Fig. l on a the left, show acomplete code telegraph picture transmission system. The picture whichis to be reproduced is in the form of a negative film 10 of varyingtransparency mounted on the drum ll of transparent material. A beam oflight from source 12 isfocussed upon a small spot on the film by meansof the lenses l3 and 14 and, after pass- 3 ing through the film,impinges uponthe photoelectric cell 15. The drum 11 on which the pic-10o ture film is mounted is driven by motors 16 through gears 17 tocause it to rotate and at the same time move slowly in an axialdirection. The light beam impinging upon the picture film 10. thus scansthe picture along a helical path. The 0 scanning light beam isinterrupted by an apertured disc 18 driven by motor 16 through gears 19and 20. There is thus produced in the circuit of the photoelectric cell15 a pulsating current hav ing an alternating component, the frequencyof plitude.

' what lighter tone value is being scanned the alall four vacuum tubes30 to 33 operate.

which is controlled in accordance with the rate of interruption of thelight beam and the picture amplitude of which varies in accordance withthe tone values of the successively scanned elemental areas of thepicture. The photoelectric current is amplified by the vacuum tubeamplifier 21 in the anode circuit of which is a circuit comprising acondenser 22 and the primary winding of transformer 23 tuned to thefrequency of the alternating component of the photoelectric current. Thesecondary winding of transformer 23 is connected to an alternatingcurrent amplifier com,- prising vacuum tubes 24 and 25, transformers 26and 27 and an adjustable attenuator 28. The output circuit of theamplifying vacuum tube is connected through transformer 29 to the inputcircuits of amplifying vacuum tubes 30 to 33, in clusive. These vacuumtubes have different grid biasing potentials and different anodepotentials, respectively, so that the operation of different tubes,respectively, is initiated in response to different values ofalternating signaling current transmitted through the transformer 29.The grid of vacuum tube 30 isbiased by the electromotive force ofbattery 34; the grid of vacuum tube 31 is biased by the sum of theelectromotive tubes 30 to 33, inclusive, also have different sources ofanode potential, the tube 30 having the anode potential equal to theelectromotive force of battery 38, tube 31 having the sum of theelectromotive forces of batteries 38 and 39, tube 32 the sum of theelectromotive forces of bat teries 38, 39 and 40 and tube 33 having theelectromotive forces of batteries 33 to 41, inclusive. When an elementalarea of the negative picture representation 10 of relatively dark tonevalue is being scanned, the transmitted alternating current and thecorresponding alternating electromotive force impressed upon the inputcircuits of vacuum tubes 30 to 33, inclusive, is of low am As a result avarying current is caused to flow in the primary Winding of transformer42 and a corresponding alternating electromotive force induced in thesecondary winding of this transformer. When an elemental area ofsometernating electromotive force impressed upon the input circuits ofvacuum tubes 30 to 33 is of correspondingly greater amplitude and vacuumtubes 30 and 31 are operated to cause an electromotive force to beinduced in the secondary windings of transformers 42 and 43. When thetone Value of the elemental area being scanned is still lighter, vacuumtubes 30 to 32, inclusive operate and for elemental areas of very lighttone value When vacuum tubes 30 to 32, inclusive operate an alternatingelectromotive force is induced in the secondary windings of transformers42 to 44, inclusive and when all four vacuum tubes operate analternating electromotive force is induced in the secondary windings ofall four transformers 42 to 45, inclusive. We may therefore consider thetone values of the picture as being grouped into four ranges of value,for example, very dark, dark, light and very light, and one, two, threeor all four of the vacuum tubes 30 to 33 will be operated according tothe group into which the tone value of the elemental area being scannedis classified. Each of these groups may be subdivided into as manygroups as desired, for example, four. It is apparent that not only willone, two, three or four of the vacuum tubes 30 to 33 be operated aselemental areas falling in different groups of tone values,respectively, are being scanned, but also that the alternatingelectromotive forces induced in the secondary windings of transformers42 to 45, inclusive, vary over a range of values in accordance with thevariations in tone value occurring within each of the four groups oftone values.

The secondary windings of transformers 42 to 45, inclusive, areconnected to the input circuits of four different groups of rectifiervacuum tubes, respectiveh, the first group comprising vacuum tubes 46 to49, inclusive. Relays 5G to 53, inclusive, are connected respectively inthe anode circuits ofrthe vacuum tubes 46 to 49, inclusive. Therectangles 54 to 56, inclusive, designate groups of rectifier vacuumtubes, having electromagnetic relays connected in the anode circuitsthereof, similar tothe group of rectifier vacuum tubes 46 to 49,inclusive, and the electromagnetic relays to 53, inclusive. One or moreof the rectifier vacuum tubes 46 to 49, inclusive, will be operatedwhenever the amplifier vacuum tube 30 is operated, one or more of thesecond group 54 whenever the vacuum tube 31 is operated, one or more ofthe third group whenever the vacuum tube 32 is operated, and one or moreof the fourth group 56 whenever vacum tube 33 is operated. The vacuumtubes of each group are provided with different grid biasing and anodepotentials, respectively, similarly to the vacuum tubes 30 to 33,inclusive, so that they operate to cause the anode current to reach apredetermined amplitude in response to input signal electromotive forcesof different amplitudes, respectively. Suppose, for example, that ablack or very dark elemental area of the negative picture 10 is beingscanned and the attenuation of the variable attenuator 28 isprogressively reduced until current flows in the anode circuits ofvacuum tubes 30 and 46, the current in the anode circuit of the vacuumtube 46 having sufficient amplitude to cause the operation of relay 50and the closure of the circuit through contact 57. As elemental areas oflighter tone value are scanned, the current in the anode circuit ofvacuum tube 30 will increase in amplitude until vacuum tube 47 and itsassociated relay 51 are operated to close contact 58, in addition tovacuum tube 46 and relay 50. As further increases in current in theanode circuit of vacuum tube 30 take place vacuum tubes 46, 4'7 and 48and relays 50, 51 and 52 will be operated to close contacts 5'? to 59simultaneously and for a still further increase in current vacuum tubes46 to 49, inclusive, and relays 56 to 53, inclusive, will operate toclose contacts 57 to 60. When an elemental area of still lighter tonevalue isthe range of tone values of each of the groups. I

When a black or very dark elemental area is scanned relay 50willoperate, when an elemental area of slightly lighter tone value isscanned relays 50. and 51 will operate simultaneously, etc.

until all of. the relays. are operated simultaneously.

in response to the scanning of 8, V8Iy light or whiteelemental area. i iWhen one or more of the relays 50, 51, 52, etc. are operated, a circuitis completed from ground 61 through one or more of. the leads 62 to .66,inclusive, through one or more of the punch magnets l to 5, inclusive,of the tape periorator 67, to the grounded battery 68, thus causing theoperation of diiferent combinations of punch magnets 1 to 5 inaccordance with the operation of the relays 50, 51, 52, etc., andpunching code combinations in tape 69 in accord-. ance with the tonevalues of the successively scanned elemental areas of the picture 10.The motor 16 which drives the drum 11 and the light interrupting disc 15also drives a cam operated punch 70 through gears 71 for punching thetape 70 with code combinations corresponding to the tone values of thesuccessive elemental areas of the picture 10, one code combination beingpunched each time the light interrupting disc 18 makes a singlerevolution. 1

The tape 69 is fed into a tape transmitter'72 which transmits codetelegraph signals corresponding to the code punchings in the tape, overa telegraph conductor 73 such as a submarine cable, for example. Insteadof punching a tape for controlling the transmission of code signalsover, a line, the code combinations may be set up by means of relaystaking the place of the punch magnets l to 5 which, together with acommutating device may control the transmission of the code signalsdirectly without first punching a tape.

Any suitable system may be employed for re producing a picture undercontrol of the received code telegraph impulses. At the receivingstation shown in Fig. 2, the code telegraph signals sent over line '73are impressed upon a tape reperforator '14 for controlling the punchingof code signals in a tape '75 to correspond with the punchings or" tape69 at the transmitting station. The tape 75 isfed into a tapetransmitter '76 which is similar to the transmitter 72 at thetransmitting station, for producing code signals which are impressed onone or more of the re lays 101 to 105, inclusive, of the switchingcircuit 7'7 in accordance with the operation of the contacts of the tapetransmitter 76. The combination of relays 101 to 105, inclusive, whichare resistance elements 150 to 165, inclusive, are

short-circuited in accordance with thecombination of relays 101 to 105whichare energized, the number of short-circuited resistance elementscorresponding to the number ofrelays 50, 51, 52, etc. which areenergized at the transmitting station. g

The number of resistance elements which are short-circuited controls theamplitude of the current from a suitable source flowing through a lightvalve 166 to control the size of the light aperture therein. The sourceof current for actuating the light valve may, for example, be a sourceof alternating current 167 having a period which is low compared withthe time required for reproducing a single elemental area of a picture.The tape 75 is fed into the tape transmitter 76 for producing currentimpulses in relays 101 to 105 at a desired rate and a picture drum 168which holds a light sensitive sheet 169 is driven at a'correspondingrate under control of a driving motor 170 and the gears 171 and 1'72,respectively. Light from source 173 is directed upon a small spot oflight sensitive sheet 169 at any particular instant by means of thelenses 174 and 175. The picture drum is caused to rotate and at the sametime to move slowly in an axial direction, similarly to the drum 11 atthe transmitting station, to cause the successively illuminated spots onthe picture receiving surface to describe, in eiiect, a helical path.The intensity of the light reaching successive elemental areas of thepicture receiving surface 169 is controlled in accordance with theamplitude of the current flowing through the light valve 166 which inturn is controlledin a cordance with the received code signals whichdetermine the number of resistance elements 150 to 165 which becomeshortecircuited by the action of the relays 101 to 105. A positivepicture corresponding to the negative picture 10 which is scanned at thetransmitting station is therefore producedon the light sensitive surface169. If desired, the relay circuits which control the shortcircuiting ofone or more of the resistance elements 150 to 165 may be rearranged sothat a negative picture is produced from a negative of the originalpicture, or so that a positive picture is produced from a positiveoriginal. The switching circuit comprising the relays 5'0, 51, 52, etc.at the transmitting station and the switching circuit 77 comprising therelays 101 to 105 at the receiving station are described in greaterdetail in the copending application of J. H. Bollman referred to above.

A disc 18 for interrupting the scanning light beam is preferably of thetype shown in Fig. 3. This disc is of opaque material and has a largenumber of closely spaced light apertures 80 arranged along a circularpath near the periphery of the disc. The apertures are preferablyomitted from a portion 81 from the disc which is large compared with thedistance between adjacent apertures-80 for the purpose of interruptingthe scanning light beam for a comparatively long period between thescanning periods of adjacent elemental areas of the picture. Thisinterruption of the scanning light beam for a compara tively long periodpermits the relays 50, 51, 52, etc. to be restored to the unenergizedcondition prior to the scanning of each elemental area or" the picture.The possibility of the incorrect operation or releasing of relays, aswhen elemental areas of only slightly dii'ierent'tone values are beingscanned in succession is thus reduced. By the use of a lightinterrupting disc of this type there is produced in the circuit of thephotoelectric cell 15 and in the transmission circuit connected to thecell a current having an alternating component having amplitudevariations controlled in accordance with the tone values of successivelyscanned elemental areas of the picture 10 and other amplitude variationswhich are independent of the tone values of the elemental areas.

What is claimed is:

1. The method of electro-optical transmission which comprises producinga current having an alternating component having amplitude variationscontrolled in accordance with the tone values of successively scannedelemental areas of a field of view and other amplitude variations whichare independent of the tone values of said elemental areas and which arerecurrent at a predetermined fixed frequency, and utilizing both saidamplitude variations to control the production of a current of differentwave form representative of said ton values only.

2. An electro-optical system comprising means for producing a, currenthaving an alternating component having amplitude variationscorresponding to the tone values of successively scanned elemental areasof a field of View and other amplitude variations recurring at apredetermined fixed frequency which are independent of the tone valuesof said elemental areas, means controlled by both said amplitudevariations for producing a different current representative of said tonevalues only and means responsive to said last mentioned current forcontrolling the production of an image of said field of view.

3. An electro-optical system comprising means for producing a currenthaving an alternating component having amplitude variationscorresponding to the tone values of successively scanned elemental areasof a field of View and other amplitude variations which are independentof the tone values of said elemental areas, means controlled by bothsaid amplitude variations for controlling the production of codetelegraph signals, and means responsive to said code telegraph signalsior controlling the production or" an image of said field or" view.

4. An electro-optical system comprising means for producing a currenthaving an alternating component having amplitude variationscorresponding to the tone values of successively scanned elemental areasof a field of View and other amplitude variations which are independentof the tone values of said elemental areas, and means controlled by bothsaid amplitude variations for producing a code telegraph recordcorresponding to the tone values or said elemental areas.

5. In an electro-optical image producing system, a source of radiantenergy, means for di recting radiant energy from said source uponelemental areas in succession of a field of view, an image of which isto be produced, and means for non-uniformly interrupting the radiantenergy from said source directed upon said field of view during thescanning period of each elemental area.

6. In an electro-optical image producing system, a source of light,means for directing a beam of light from said source upon a field ofview,

an image of which is to be produced, light responsive means forreceiving light from said field of view for controlling the productionof image current having a characteristic determined by the tone valuesof elemental areas or" said field of view, and means for non-uniformlyinterrupting the light beam from said source directed uponsaid field or"view during the scanning period of each elemental area.

'7. In a code telegraph image transmission system, means for controllingthe production of an image current, said means comprising means forproducing a beam of radiant energy, an electromagnetic relay theoperation of which iscontrolled in accordance with said image .current,

and means for periodically interrupting said beam of radiant energy fora period of sufiicient duration to cause said relay device to berendered inoperative.

8. In a code telegraph image transmission system, means for controllingthe production of an image current, said means comprising means forproducing a beam of light for scanning the elemental areas of a field ofview in succession, a plurality of electromagnetic relay devices whichare adapted to be operated selectively in accordance with acharacteristic of said image current, and means for interrupting saidlight beam following the scanning period of each elemental area for aninterval of sufficient duration to cause said electromagnetic relays tobecome inoperative during said interval.

9. In a code telegraph image transmission system, means for controllingthe production of discontinuous impulses of periodically varying imagecurrent, each impulse corresponding to the tone value of an elementalarea of a field of view, and means under control of said impulses ofvarying'image current for controlling the production of current impulsesof substantially constant amplitude to control the production of animage.

10. In a code telegraph system, means for intermittently producingimpulses of periodically varying current, each impulse corresponding tothe tone value of an elemental area of a field oi view, and means undercontrol of said current impulses for producing current impulses ofsubstantially constant amplitude for controlling telegraph apparatus.

11. In a code telegraph system, means for periodically producingimpulses of periodically varying current, each impulse corresponding tothe tone value of an elemental area of a field of view, and means undercontrol of said current impulses for controlling the punching of codecombinations in a tape in accordance with amplitude variations of saidcurrent impulses.

12. In a code telegraph system, means for intermittently producingimpulses of alternating electromotive force, each impulse correspondingto the tone value of an elemental area of a field of view,'said impulseshaving different amplitudes in accordance with a signal to be produced,means for producing, under control of said alternating electromotiveforce, code telegraph signals comprising impulses of relatively steadycurrent.

13. An electro-optical image producing system comprising a source oflight, means for directing light from said source upon elemental areasin succession of a field of View, an image of which is to be produced,means responsive to light received from said field of View forcontrolling the production of periodic impulses of alternatingelectromotive force, said impulses having differentamplitudes, eachimpulse corresponding to the tone value of an elemental area of saidfield of View, means for producing code telegraph signals under controlof said impulses of alternating electromotive force, and meansresponsive to said code signals for controlling the production of animage of said field of view.

' JOSEPH W. HORTON.

